1. Field of the Invention
The present invention relates to digital photography. In particular, the described embodiments relate to digital imaging arrays.
2. Related Art
Digital cameras have enabled the convenient transfer of still images to computer readable memory. A digital camera typically includes a lens which focuses light reflected from objects onto an electronic imaging array. An image exposure is then captured onto a computer readable memory, allowing for the convenient reproduction of the image by a color printer which may be part of a personal computer system.
The imaging array typically includes a plurality of pixels or light sensitive elements. By use of appropriate filters, the pixels are made sensitive to energy in particular color bands or spectral regions. For example, a typical imaging array has three sets of pixels, each pixel being sensitive to one of red light, blue light and green light. Such an array is described in detail in U.S. Pat. No. 3,971,065 to Bayer. These imaging arrays typically form a mosaic pattern which uniformly distributes each of the three sets of pixels over the array. The individual pixels in the array sense the intensity of light in specific spectral regions at specific locations in the imaging array. This enables the reconstruction of the image using techniques known to those of ordinary skill in the art.
Conventional imaging arrays comprise charge coupled devices (CCDs) to convert a pixel of light energy into charge. The charge is stored in a capacitor formed in the imaging array at the pixel location. The quantity of stored charge is proportional to the energy received at the pixel location over an exposure period. Additionally, imaging arrays have been constructed from active pixel sensor (APS) cells to convert light energy into an electric voltage at a photodiode. Circuitry for implementing APS cells is shown in U.S. Pat. Nos. 5,471,515 and 5,587,596. The APS cell imaging arrays can be integrated into a CMOS imaging chip, i.e., integrated circuit.
The circuitry for all of the pixels in an imaging array is typically uniform regardless of the color of the individual pixels. CCD and APS imaging arrays typically cannot identify the wavelength or color of light detected at a particular pixel based solely upon the electrical signal generated at the output of the pixel. Color selectivity is provided by controlling the color of light that is allowed to reach a photo detector. One typical method includes directly depositing transmission filters onto substrate areas where individual pixels are located. The filter color pattern deposited on a given pixel element in the imaging array controls the color of light that is detected by that particular pixel. Thus, while the optics produce an image which has the same color depth at each point of the image, the image incident on the imager collects only one color at each pixel location. If red, green and blue are used as the primary colors, a typical imaging array will have individual pixels with a red, green or blue filter deposited thereon. A typical system is described in detail in the aforementioned U.S. Pat. No. 3,971,065.
Digital cameras employ several methods for extracting the pixel data from the imaging array. For a CCD based array, the charge stored at the pixel locations in the array may be sequentially transferred to the capacitors of neighboring pixels, one pixel at a time, until the charge reaches a read-out circuit for quantizing the charge at an edge of the array. For example, in some systems, the charges stored at each pixel location may be simultaneously shifted in a direction toward the read-out circuitry.
For an APS based array, the voltages at the photodiodes may be coupled directly to the read-out circuit. The voltages for the individual pixels are typically readout one row at a time by applying a row selection signal to a row of pixels, while the read-out circuit receives the corresponding voltages from each pixel in the row.
Existing read-out circuitry generates mixed color data. Readout techniques for extracting data from an imaging array having a Bayer pattern typically provide mixed color data in which blue pixel data is interleaved with green pixel data, and red pixel data is interleaved with green pixel data. The mixed color data is typically stored in a memory to be processed later in a digital image processor. Certain image processing techniques require color processing which utilizes algorithms applied to all pixels of a particular color. This requires sorting of the mixed color data stored in the memory. This increases processing requirements at the image processor which contributes to increased cost, power consumption and weight of a digital camera. Therefore, there is a need for facilitating color extraction which reduces the requirements for processing at a digital image processor.
An object of an embodiment of the present invention is to provide an architecture for the efficient extraction of data from photo sensors.
Another object of an embodiment of the present invention is to provide a system and method for extracting data from photo sensors which reduces processor and memory requirements for digital cameras.
It is another object of an embodiment of the present invention to provide a system and method for simplifying color processing in digital cameras.
It is another object of an embodiment of the present invention to reduce the cost, weight and power consumption of digital cameras.
It is yet another object of an embodiment of the present invention to provide a system and method for grouping information extracted from pixels on an imaging array by color.
Briefly, an embodiment of the present invention is directed to a system for extracting data from an array of light-sensitive elements. Each of the light-sensitive elements is sensitive to energy in one of a plurality of spectral regions. An extraction circuit extracts data representative of the intensity of photo-exposure of each of a plurality of the light-sensitive elements in extraction intervals. The data extracted in each extraction interval at the extraction circuit originates from light-sensitive elements associated with a common spectral region (e.g., red).
Accordingly, all signals extracted at the extraction circuit in any particular extraction interval are representative of photo-exposures of the light-sensitive elements which are sensitive to energy in the same common spectral region. This enables uniform color processing on data read out from the extraction circuit following an extraction interval. This reduces the requirements for digital processing which in turn reduces manufacturing costs, weight and power consumption of a digital camera.